Projection light intensity control mechanism



i r Nov 29 1932. a. MARKS PROJECTION LIGHT INTENSITY CONTROL MECHANISMFiled Nov. 23 1951 3 filzeeis-Sheet Nova 29, 1932. E. MARKS 193399149PROJECTION LIGHT INTENSITY CONTROL MECHANISM Filed Nov. 25, 1,951 5Sheets-Sheet 2 VENTUR:

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PRDJEC'ZZQN LIGHT INTENSITY CONTROL MECHANISM Filed NOV. 25, 1951 ATTEIRNEH I rsmoar. or season,

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is not being operated to feed the tion of gravit Patented Nov, 1932 TaoSTATES IABSACH USETTS, A SSIGNOB TO KEYSTONE MTG. 00., O]

BOSTON, MASSACHUSETTS jidruomcrrozr LIGHT mmrsm coarser. u'ncnamsxApplication flied November 28, 1931. Serial No. 578,779.

This invention relates to improvements in a motion picture projector andmore particularly to a light controlling mechanism which automaticallydecreases the intensity of light, focused by the condensing lens, ontothe film in the film gate when the gro ector 1m strip forward, but whichallows the full intensity of the light to strike the film when said filmstrip is bein fed forward at" even a fairly slow rate 0 speed.

When a. bright light is focused sharply on ,a motion picturefilm stripas in a pro ector,

the film Wlll be burned or istered if allowed to remain stationary foreven a few seconds. In usual practice, where 16 pictures a second areprojected, the film is stationary only about 1/20 of one-second and thelight is cut as by the shutter durin part of this period so there is nodanger of urning unless excessive light is used.

The picture ma be focused more sharply on the screen, if is focusin isdone while the film is stationary in the lm gate. It is also founddesirable at times to project still pictures, especiall with the amateuror home. projector, where t e scenes are usually short and it is desiredto study an especially interesting portion by stopping the projectorwith the shutter open. To prevent injury to the film in such cases, isthe object of this invention.

To accomplish this, there is provided a dimmer arm of light weight,pivoted on the body of the projector and havin a wirescreen, mesh at oneend, which un er the actends to cover an opening through whic the lightpasses from the li ht source to the film in the film te. There is aflexible projection on the si eof the dimmer. arm w ich is engaged bprogections on the usual multiple blade s utter,

ocat'ed just back of the immer arm, and between it and the light source.The pro'ections on the shutter are located so that t ey strike theprojection on the dimmer arm, just asthe shutter blade has cut off thelight to id the wire screen is pushed out of no 'ght p to the film. Asthe shutter continues to revolve and just before the shutter bladeallows the light to pass the projection on the dimmer arm slips oil theprojection on the shutter and due to gravity the Wire screen falls infront of the opening through which the light passes and obstructsglportion, causing less lightto fall upon the There is a certain amountof time required for the wire mesh to fall and it is found that evenwhen the shutter is rotated at a comparatively slow rate of speed,before the wire mesh begins to obstruct the light, the followingprojection on the shutter, strikes the projection on the dimmer arm andthe wire mesh is prevented from falling.

Thus, if the shutter is rotated as in re lar projection, the light isnot obstructe but falls with full-intensity on the film. If the shutteris stopped with the blades in position to let the light pass, the dimmerscreen falls into the path of the light, dimming the light on the film.Since in regular projection, the shutter periodically intercepts thelight, the still p1cture will appear on the screen as bright asthemovingpicture.

A metal blade with a few comparatively large holes would cause the sameefiect of dimming, but when using the projector at Lamps of 'difierentintensity require wire mesh of difierent spacing of wires for bestresults.

Since the of s eed, its projections continuously hit the flexibleprojection on the dimmer-arm, but due to the flexibility of thisProjection and the light weight of the arm, the action is practicallynoiseless and the arm remains comparatively stationary in a tiltingposition.

A more particular description of the invention is as follows:

shutter revolves at a high rate v with an idler gear 8 on pivot 9. Thiscut away to show the light intensity control mechanism.

Figure 2 is aside elevation, partly in section, showing a side view ofthe above mechamsm.

Figure 3 is a. section of Figure 1, on line 33.

Figure 4 is a back view of the shutter, showing the control mechanismarm. in dotted lines with the obstructing screen in the path of thelight.

Figure 5 is a front view of the shutter, showing the control mechanismin elevation when the obstructing screen is pushed out of the path ofthe light.

Figure dis a side view of the shutter, partly in section, showingcontrol mechanism in side elevation.

Figure 7 is'an enlarged view showing the means of fastening of flexibleprojection to the control mechanism arm.

. Similar reference numerals indicate lik parts in the several views.

Referring to the drawings, 1 is the projector body on which is mountedthe various parts of the projector. 2 isthe lamp house, containing aprojection lamp 3 andcondensing lens 4. The shutter 5 is mounted onshaft 6, on which is also fastened the cam which'drives the intermittentfilm feeding mechanism and a pinion 7 meshing idler meshes with thelarge gear 10 on shaft 11. On the other end of shaft 11 is thecontinuous feed sprocket 12. The large gear 10, has fast to it the lowerreel drive ulley 13 which through take-up belt 14 rives the take-upulley 15 on shaft 16, on which is the ower reel 17. The

upper reel 18 supplies the film to the continuous feed sprocket 12,which delivers the film to the film gate 19 and intermittent feedingmechanism. The light beam is pro'ectedfrom the projection lamp 3 thronga condensing ens 4, past the shutter 5 through a second condensing lens20 to a mirror 21, which reflects the light at right angles through theaperture and film in the film gate 19, to the projection lens 22, andfrom thence to the screen.

Between the shutter 5 and the second condensing lens 20 is the dimmerarm 23, pivoted on the bodyat 24 with a wire mesh screen 25 at its upperend. The lower end of 23 has an extension 26, so that due to the forceof gravity the screen 25 is forced to the right, as looked at from thelamp house side. This movement is arrested when the screen isin-alignment with the second condenser 20 by the side of the dimmer armstriking a projecting back into the beam of light. 33

.Patent is:

hubon the body 1.

When the screen 25 is forced to the left out of alignment with condenser20 and the beam of light, its movement is arrested by the projection 27on the dimmer arm strikin the under side of said hub. .At 28 on thedimmer arm is attached a flexible projection 29, composedof a coil offine wire. This coil is fastened end-ways to the dimmer arm by twohollow rivets. The outer rivet 37 acts as a spacer. The inner rivet 38passes through this and the arm and is riveted to the arm. The coil ispushed through the inner rivet and the sides of both rivets are squeezedtightly against the coil 29. The three blade shutter 5 has three camshaped projections 30, which are in such position with the shutteropenings that just as a shutter blade has cut off the light fromcondenser 20, a projection 30 strikes the projecting coil 29 and forcesscreen 25 out of the path of the light. As the shutter revolves to theleft and just before the blade 31 allows the light to pass to condenser20, the coil 29 slips by the end 32 of the projection 30 and due togravity the screen 25 is swung is the base of the machine, 34 is a motorto drive it,

35 is a rheostat'housin'g in which is the rheostat with control knob 36.

..Having thus described the invention, what I claim as new and desireto 1. In a motion picture machine, the combination of supply and take-upreels, a continuous feed sprocket, an intermittent film feedingmechanism, a film guide with aperture'opening, in alignment with aprojection lens and light source, a rotatable shutter, whichintermittently cuts off the light from said light source to saidaperture and a light intensity control mechanism, adjacent to saidshutter, having a pivotally mounted arm, carrying a light obstructingmember of fine wire mesh, held by gravity, in the path of said light andoperated automatically to control the intensity of light falling fromsaid light source on said aperture, by cam shaped projections on saidshutter engaging a fiexile projection on said arm, all substantiallytially as described.

2. In a motion picture machine, the combination of supply and take-upreels, a continuous feed sprocket, an intermittent film feedingmechanism, a film guide with aperture secure by Letters feedingmechanism,

of which is inserted into a hollow rivet, which is passed through asecond slightly larger hollow rivet, to act as a spacer, the firstrivet, then being riveted to a member of the control mechanism and thesides of the rivets tightly pressed to the wire coil, all substantiallyas described.

3. In a motion picture machine, a combination of supply and take-upreels, a continuous feed sprocket, an intermittent film a filmguide-with aperture opening, in alignment lens and light source, arotatable shutter, intermittently, intercepting said light, and a lightintensity control mechanism, composed of a light weight, partiallybalanced, pivoted arm, having a light obstructing screen at its upperend, held by gravity, in the path of the light from shutter to apertureopening, and easily moved out of said path by projections on and insynchronism with the blades of said shutter, consecutively striking ashock absorbing, flexible projection on sai arm, all substantially asdescribed.

ISIDORE MARKS.

with a projection

